Mother/earthbound started out on the NES where it gained something of a cult following. The long awaited third entry in the series hit on the GBA and never made it out of Japan, previous titles in the series also command a high price second hand and Nintendo had previously been somewhat reluctant to rerelease them outside Japan (or at least until the other week). In one of the more impressive translations the GBA has seen it was translated by the folks at Fobby.net.
An English reproduction of Mother 3 is now available though we can not link it up on this site as it is completely unlicensed. For those that don't know, a reproduction is usually a fan-made cartridge with original parts. Unlike previous Mother 3 reproductions which were made in batches of 10 at most, this one is not made of gutted flash cart parts.
If you're asking why someone would want this when there are GBA flash carts I can give you a few reasons. One benefit of a dedicated card is no SD slot and a form factor that fits flush with a Gameboy Advance. There is also no menu or splash screen; you boot right to the game which is only functionally comparable to an EZ 3-in-1 or X-ROM 512 in single game mode. Also it's an English Mother 3 cartridge.
It is sold cart-only, I believe with a label. If you want a box your options are here or here.
I'm not totally sure this news works for GBAtemp, but it's more fitting with the site's theme than cell phone benchmarks for example. If a mod has a problem with it please move it somewhere more fitting.